1. Field of the Invention
The present invention relates to an intake system for an internal combustion engine and more particularly to an engine intake system having a primary and secondary intake passages. More specifically, the present invention pertains to fuel supply means for an engine intake system having primary and secondary intake passages.
2. Description of Prior Art
In automobile engines, it has been proposed to provide primary and secondary intake passages leading to the same combustion chamber so that the intake air is introduced only through the primary intake passage under certain engine operating conditions but through both the primary and secondary intake passages under other engine operating conditions. For example, in Japanese patent application No. 50-7740 filed on Jan. 20, 1975 and disclosed for public inspection under the disclosure No. 51-83934, there is disclosed an engine having a primary intake passage and a secondary intake passage which are connected to the same combustion chamber. The secondary intake passage is closed under a light load engine operation so that the intake air is passed only through the primary intake passage, but the secondary intake passage is opened under heavy load engine operation so that the intake air is passed through both the primary and secondary intake passages. The primary and secondary intake passages are respectively provided with fuel injection valves and fuel is injected only through the fuel injection valves provided in the primary intake passage under light load engine operation, whereas both the fuel injection valves in the primary and secondary intake passages are used under heavy load operation.
In the engine of the aforementioned type, the control of the secondary intake passage is usually made under the engine intake pressure and the total fuel supply is shared by the fuel valves in the primary and secondary intake passages when the secondary intake passage is opened. In determining the quantity of fuel supply, calculation is at first made in accordance with the engine operating condition to obtain a basic injection period signal which is thereafter modified in several respects to obtain a valve actuating signal. Under light load operation wherein only the primary intake passage is used, the valve actuating signal is applied only to the fuel injection valve in the primary intake passage. However, under heavy load operation, wherein both the primary and secondary intake passages are used for supplying the intake air, the valve actuating signal is shared by the fuel injection valves in both intake passages.
It has been found in this type of intake system that a desired air-fuel ratio cannot be obtained in the transient period wherein the second intake passage is being brought into full operation. In other words, when the fuel supply system is adjusted so that an appropriate amount of fuel is supplied under a first engine operating condition, such as light load operation, the quantity of the fuel supply becomes greater than an optimum value in a transient period wherein the second intake passage in partially opened. On the other hand, if the fuel supply is optimum when the second intake passage is partially open, the fuel supply under the first condition will become smaller than the optimum value. This phenomenon is caused by the fact that the intake suction pressure is stronger in the secondary intake passage than in the primary intake passage, although the difference may be very small, so long as the secondary intake passage is not fully open and the quantity of fuel supply is affected by the suction pressure in the intake passage to which the fuel injection valve is exposed.
In order to solve the problem, there may be provided independent fuel pressure regulators respectively for the fuel injection valves in the primary and secondary intake passages, so that the fuel pressures applied to the respective valves are controlled in response to the intake suction pressures in the corresponding intake passages. It should be noted however that the solution is not advantageous because it requires a plurality of fuel regulators and spaces therefor.